This invention relates to articles of footwear having improved cushioning, comfort and stability. Particularly, this invention relates to articles of footwear that include cushioning devices which provide superior comfort to a wearer and provide superior performance under high loading conditions.
Articles of footwear have long been studied and redesigned to achieve enhanced comfort and performance. In this regard, and particularly in athletic shoes, primary concerns include the ability to provide the foot with a comfortable environment and to mitigate the shock or impact experienced when the shoe and, accordingly the foot and lower leg, impact the ground or floor. These forces are particularly significant during running and jumping. For example, a jogger landing on four or five square inches of the heel is estimated to absorb an impact force of about three to four times the weight of the jogger. Accordingly, a jogger of 180 pounds may create an approximate force of 720 pounds of shock on the heel landing area. Since each heel could impact the ground about 800 times per mile, it is easy to see the necessity of a shock absorbing mechanism in footwear.
In addition to a shoe absorbing intense and repeated impact, the criticality of comfort is readily understood by everyone who wears shoes. In fact, comfort in athletic shoes is known to effect the wearer""s psychological state, and therefore, his or her performance, muscular efficiency, energy consumption, and the athlete""s ability to train and compete.
A variety of elastomeric materials, including natural rubber, polymerized and copolymerized elastomers, and synthetic rubbers have been used in shoe construction to absorb these forces. However, these elastomeric materials suffer degradation from repeated use and have relatively poor energy transfer efficiency characteristics. Accordingly, the industry has searched for alternative means of foot cushioning.
In this search, pneumatic cushioning devices have long been studied. For example, U.S. Pat. No. 259,092 (1882) demonstrates a very early pneumatic sole. Notwithstanding the long search, pneumatic cushioning devices failed for nearly a century and for a variety of reasons to achieve commercial success. In fact, until the inventions described in U.S. Pat. Nos. 4,183,156 and 4,219,945 were made, the art lacked the technological know-how to make pneumatic cushioning in shoes commercially successful. The inventions described in these patents revolutionized shoe design and the athletic footwear market place, having been incorporated into at least 200 million shoes sold worldwide.
Following this initial success of pneumatic cushioning, several attempts to improve these systems have been made. U.S. Pat. No. 4,506,460, for example, discloses a moderator device which functions in combination with either elastomeric or pneumatic cushioning elements. The moderator is used to absorb, redistribute, store and return energy. U.S. Pat. No. 5,083,361 describes a shoe including a stacked air chamber arrangement. In this design, the air chambers are constructed with an outer barrier layer of elastomeric material with drop-linked fabric to average stress of the chambers and maintain stability. It is also suggested to inflate the top chamber to a lower pressure in order to provide initial contact softness.
Taiwanese Application No. 75100322 discloses an outboard double deck air cushion where the peripheral air chambers in the top unit and the peripheral air chambers in the bottom unit are in fluid communication. The central air chambers of the top air cushion and those of the bottom air cushion are also in fluid communication. This design is intended to provide an air insert which continues to support the wearer after being punctured. For that purpose, the design includes a piercing proof sheet material such as a light metal between the first and second air cushions to prevent puncture of the upper cushion. However, this design, by allowing fluid communication between the top and bottom air cushions, may be unstable as a result of rapid, almost instantaneous, dispersion of air pressure under a load applied to localized areas. More particularly, this design appears to act more like a thick single cushion insert than two separate units. In fact, it is believed that this design leads to xe2x80x9cbottoming outxe2x80x9d of heavily loaded chambers and the simultaneous ballooning of unloaded chambers, causing instability when an uneven force is applied to the plantar surface of the foot of the outsole of the shoe. This instability termed herein a xe2x80x9ctennis ballxe2x80x9d effect appears to be particularly true when the cushions total more than 0.800 inches in thickness. Accordingly, this design presents an injury risk and fails to provide the advantage of superior comfort and superior performance in an article of footwear.
As is apparent from the above description of the art, a need exists for a cushioning system which provides both the comfort and performance benefits of fluid cushioning. This invention provides a means to achieve several very important goals; superior comfort in a shoe in combination with superior technical performance and lightness of weight.
In accordance with the purpose of the invention as embodied and broadly described herein, the article of footwear of this invention comprises a shoe upper shaped to envelop and cushion the foot. The upper is attached to a sole having a ground engaging portion. A first sealed elastomeric member containing a fluid is positioned in the article of footwear between at least a portion of the foot and the ground engaging portion of the sole. A second sealed elastomeric member containing a fluid is positioned between the foot and the ground engaging portion of the sole, with at least a portion of the first member overlapping the second member. A load distributing element is positioned between the first and second members, intermediate at least a portion of the overlapping region of the members.
The first member of this shoe is preferably located within the shoe""s foot constraining envelope, and is termed xe2x80x9cinboardxe2x80x9d for purposes of this disclosure. This location provides exceptional point-of-sale appeal, because the fluid containing cushion insert is in direct elastomeric proximity with the plantar surface of the foot, providing the wearer with a clear xe2x80x9criding-on-airxe2x80x9d sensation (in the case of air filled inserts). Preferably, the sewed elastomeric member is located in the sole of the shoe, exterior and below the shoe upper envelope easing the foot, and is termed xe2x80x9coutboardxe2x80x9d. This cushion is preferably designed to absorb and beneficially redistribute, store and return significant impact forces.
Accordingly, an article of footwear is described with a fluid containing elastomeric cushioning device adjacent the foot and a fluid containing elastomeric cushioning device more proximate the ground engaging surface of the shoe. In certain embodiments, the fluid containing cushioning device nearer the ground engaging surface of the shoe may be constructed with one side functioning as the ground engaging surface of the shoe.
A load distributing element is located between the two cushioning devices to prevent painful and destabilizing localized forces and to facilitate load dispersion across the cushioning devices, increasing their effectiveness. In this preferred design, the two cushioning devices respectively provide comfort and performance and, in fact, overall superior cushioning may occur. Therefore, this invention advantageously provides a new and improved article of footwear providing both superior comfort and performance.